Turbocharger Nonlinear Response With Engine-Induced Excitations: Predictions and Test Data

Abstract

Turbochargers (TCs) aid to produce smaller and more fuel-efficient passenger vehicle engines with power outputs comparable to those of large displacement engines. This paper presents further progress on the nonlinear dynamic behavior modeling of rotor-radial bearing system by including engine-induced (TC casing) excitations. The application is concerned with a semifloating bearing design commonly used in high speed turbochargers. Predictions from the model are validated against test data collected in an engine-mounted TC unit operating at a top speed of 160 krpm (engine speed=3600 rpm). The bearing model includes noncylindrical lubricant films as in a semifloating-ring bearing with an antirotation button. The nonlinear rotor transient response model presently includes input base motions for the measured TC casing accelerations for increasing engine load conditions. Engines induce TC casing accelerations rich in multiple harmonic frequencies; amplitudes being significant at two and four times the main engine speed. Fast Fourier transfor frequency domain postprocessing of predicted nonlinear TC shaft motions reveals a subsynchronous whirl frequency content in good agreement with test data, in particular, for operation at the highest engine speeds. Predicted total shaft motion is also in good agreement with test data for all engine loads and over the operating TC shaft speed range. The comparisons validate the rotor-bearing model and will aid in reducing product development time and expenditures.